<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <script src="/JS/js/file.js"></script>
</head>
<body>
    
     <button onclick="alert('告辞')">点我</button>

    <script>
        var a = "qwertyuiop"
        let b = 2;
        const c = 3;
        alert("666")
        document.write(a.indexOf("o"))
        
        //基本类型：number boolean string 
        //特殊类型：undifined null  alert弹出框
        //对象类型（引用类型）:日期，数组，函数，对象
    </script>
</body>
</html>